Differential Diagnosis for Rash on Leg
- Single most likely diagnosis
- Eczema (atopic dermatitis): This is a common condition characterized by itchy, inflamed skin, which can appear anywhere on the body, including the legs. Its high prevalence and the fact that it can be triggered by various factors make it a likely diagnosis for a rash on the leg.
- Other Likely diagnoses
- Contact dermatitis: This condition occurs when the skin comes into contact with an irritant or allergen, leading to a rash. Given the exposure of legs to various substances (e.g., soap, detergent, plants), contact dermatitis is a plausible cause.
- Psoriasis: A chronic skin condition that speeds up the life cycle of skin cells, causing cells to build up rapidly on the surface of the skin. The legs are a common area for psoriasis plaques to appear.
- Cellulitis: A bacterial skin infection that can cause redness, swelling, and warmth of the skin, typically on one leg. It's a common condition that can be diagnosed based on clinical presentation.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Deep vein thrombosis (DVT): Although DVT presents more commonly with swelling and pain rather than a rash, in some cases, it can cause skin discoloration or a rash due to the inflammatory response. Missing DVT can lead to pulmonary embolism, which is life-threatening.
- Necrotizing fasciitis: A severe bacterial infection that destroys tissue under the skin, including fat and the tissue covering the muscles (fascia). It's rare but can be fatal if not treated promptly. Early signs can include a rash or redness of the skin.
- Meningococcemia: A severe infection caused by Neisseria meningitidis, which can lead to a rash (petechiae or purpura) as part of its presentation. It's critical to identify this condition early due to its high mortality rate if left untreated.
- Rare diagnoses
- Erythema migrans (Lyme disease): Characterized by a distinctive "bull's-eye" rash, which can appear on the leg after a tick bite. It's less common in areas with low incidence of Lyme disease but should be considered in endemic areas or in patients with a history of tick exposure.
- Cutaneous T-cell lymphoma (Mycosis fungoides): A rare type of skin cancer that can cause a rash, which may resemble eczema or psoriasis. It's essential to consider this diagnosis in cases where the rash does not respond to standard treatments.